Letterpress printing (also referred to as typography) is a known printing process (see for instance Chapter 2.3, pp. 395-408, of the “Handbook of Print Media—Technologies and Production Methods”, Helmut Kipphan (Ed.), ISBN 3-540-67326-1, Springer-Verlag Berlin Heidelberg, 2001).
Letterpress printing is in particular applied in the context of the production of security documents, such as banknotes, for the purpose of numbering the security documents, i.e. providing the security documents with one or more unique serial numbers. Letterpress printing is also typically used in security printing applications for the purpose of providing the security documents with further letterpress features such as a date (e.g. a banknote issuing date), signatures, seals and the like (see also Chapter 2.5.1, pp. 423-433, of the aforementioned handbook, especially the section on pages 427-428, entitled “Number Printing, Date, and Signatures”).
Letterpress printing presses and numbering presses are known as such in the art.
Numbering presses are for instance disclosed in European Patent Publications Nos. EP 0 061 795 A1, EP 0 167 196 A1 and in International (PCT) Publications Nos. WO 2006/129245 A2 and WO 2007/060624 A1, which are all in the name of the present Applicant and are incorporated herein by reference in their entirety.
Combined printing presses combining a letterpress printing (e.g. numbering) group and further printing or processing groups are further known in the art. International (PCT) Publication No. WO 2011/145028 A1 in the name of the present Applicant, which is also incorporated herein by reference, for instance discloses a combined numbering and varnishing press. International (PCT) Publications Nos. WO 01/85457 A1, WO 01/85586 A1, WO 2005/008605 A1 and WO 2005/008606 A1, all of which are likewise incorporated herein by reference in their entirety, further disclose variations of a combined inspection and numbering press.
Other numbering presses are also disclosed in European Patent Publications Nos. EP 0 286 317 A1, EP 1 046 498 A1, EP 1 197 332 A1, EP 2 468 506 A1, EP 2 599 631 A1, Japanese Patent Publication No. JP 2000-085095 A and International (PCT) Publications Nos. WO 2006/051563 A1, WO 2008/065693 A1.
FIG. 1 schematically illustrates a known sheet-fed numbering press as previously marketed by the Applicant under the product designation “Super Numerota® 212”. A similar illustration can be found on page 428 of the aforementioned “Handbook of Print Media”. This numbering press typically comprises a sheet feeder 1 for feeding individual sheets in succession to a letterpress printing group 2, acting as numbering group. Once printed by the letterpress printing group 2, printed sheets are typically transferred to a sheet conveyor system 3 which commonly comprises a plurality of spaced-apart gripper bars driven by a pair of endless chains and designed to hold the sheets by a leading edge thereof. This sheet conveyor system 3 transports the printed sheets along a sheet delivery path to a delivery station 4 where they are delivered onto corresponding delivery piles.
In the illustrated example, the letterpress printing group 2 comprises a two-segment impression cylinder 10 transporting the sheets in succession in front of a first letterpress cylinder, acting as first numbering cylinder, 11.1 and a second letterpress cylinder, acting as second numbering cylinder, 11.2. The numbering cylinders 11.1, 11.2 typically carry a plurality of numbering devices (or numbering boxes) which are arranged in a manner corresponding to the array of individual security prints (e.g. banknote prints) which have been printed on the sheets, prior to being fed on the numbering press. Each individual security print thus receives a unique serial number that is printed twice at distinct locations of the security print.
Each numbering cylinder 11.1, 11.2 is typically inked by a corresponding inking device 12.1, respectively 12.2. The inking devices 12.1, 12.2 supply corresponding inks (which can be different) to the letterpress printing forms of the numbering cylinders 11.1, 11.2 (namely the corresponding printing faces of the relevant numbering wheels of the numbering devices), which in turn transfer the corresponding ink patterns (e.g. in the form of a string of alphanumerical characters) onto the sheets carried by the impression cylinder 10.
FIG. 2 schematically illustrates another known sheet-fed numbering press as currently marketed by the Applicant under the product designation “Super Numerota® III”. This numbering press operates according to the same principle as the numbering press of FIG. 1 and likewise comprises a sheet-feeder 1′ feeding individual sheets in succession to a letterpress printing group 2′, acting as numbering group, to a sheet conveyor system 3′ (which likewise comprises a plurality of spaced-apart gripper bars driven by a pair of endless chains and designed to hold the sheets by a leading edge thereof), and then to a sheet delivery station 4′ where they are delivered onto corresponding delivery piles.
The letterpress printing group 2′ also comprises a two-segment impression cylinder 10′ transporting the sheets in succession in front of a first numbering cylinder (first letterpress cylinder) 21.1 and a second numbering cylinder (second letterpress cylinder) 21.2. In this example, each numbering cylinder 21.1, 21.2 is inked by a corresponding inking device 22.1, respectively 22.2, which inking devices 22.1, 22.2 are located in a corresponding inking carriage 20 that can be retracted away from the impression cylinder 10′ and the numbering cylinders 21.1, 21.2 during maintenance operations (see also International (PCT) Publications Nos. WO 2006/129245 A2 and WO 2007/060624 A1). In contrast to the numbering press of FIG. 1, the numbering press of FIG. 2 further comprises another letterpress cylinder 23 (in addition to the numbering cylinders 21.1, 21.2) located upstream of the first numbering cylinder 21.1, which letterpress cylinder 23 can for instance be used to print an additional letterpress feature on the sheets (such as a date, a signature, or the like). In contrast to the numbering cylinders 21.1, 21.2, this additional letterpress cylinder 23 can carry a suitable letterpress printing plate on its circumference. A corresponding inking device 24 is further provided to supply the letterpress cylinder 23 with the desired ink.
FIG. 3 shows a variant of the letterpress printing group 2′ of FIG. 2. Components of the letterpress printing group 2″ shown in FIG. 3 which are common with that of the printing group 2′ of FIG. 2 are designated by the same reference numerals and will not be described again.
FIG. 3 shows that the inking device 24′ used to supply ink to the letterpress cylinder 23 comprises two ink fountains 24a, 24b (rather than only one as shown in FIG. 2). The inking devices 22.1, 22.2 could likewise be modified to make use of a double ink fountain arrangement, instead of a single ink fountain 22.1a, 22.2a as illustrated. Thanks to such double ink fountain arrangements, two (or more) inks can be supplied to the corresponding letterpress cylinder 21.1, 21.2, 23 in order to print multicolour features. In particular, a first portion of the serial numbers could be inked with one ink colour, while a remaining portion of the serial numbers could be inked with another, different ink colour. With such an inking configuration, a colour-split is however only possible in the axial direction, i.e. along the direction of the axes of rotation of the cylinders 10, 21.1, 21.2, 23.
European Patent Publication No. EP 0 291 159 A1 discloses a multicolour offset printing press of the type comprising a printing group equipped with a plate cylinder carrying a letterpress printing plate, which letterpress printing plate is inked with a multicolour ink pattern transferred from an ink-collecting cylinder. This ink-collecting cylinder (also referred to in the art as “Orlof cylinder”) collects different ink patterns from multiple chablon cylinders (or “colour-selection cylinders”) that are distributed about the circumference of the ink-collecting cylinder, each chablon cylinder carrying a chablon plate with relief portions that are inked by an associated inking device. This printing process is known in the art as “Orlof-offset printing” and only involves collecting of multiple ink patterns on the ink-collecting cylinder for transfer onto a single plate cylinder, which then transfers the resulting multicolour pattern of inks onto the substrate to be printed via a blanket cylinder.
Other offset printing presses adapted to perform “Orlof-offset printing” are also known from European Patent Publications Nos. EP 0 132 858 A1, EP 0 343 105 A2, EP 0 343 106 A2, EP 0 343 107 A2 or International (PCT) Publication No. WO 2007/042919 A2.